Process of stabilizing cellulose derivatives



Patented Dec. 13 1938 UNITED STATES PATENT OFFICE PROCESS OF STABILIZINGOELLULOSE DERIVATIVES No Drawing. Original application November 22,

1937, Serial No. 175,979. Divided and this application April 27, 1938,Serial No. 204,601

15 Claims.

This is a division of my application Ser. No. 175,979, filed November22, 1937 for Process of stabilizing cellulose derivatives. I

The present invention relates to a process of 5 purifying andstabilizing saturated cellulose esters.

One object of this invention is to provide for a process of stabilizinga saturated cellulose ester by treating a crude, saturated celluloseester with 0 anhydrous, liquid ammonia.

Another object of my invention is to provide for a process ofstabilizing a crude, saturated cellulose ester by treating it withanhydrous, liquid ammonia at a temperature at which it is not decomposedby said ammonia.

A further object of this invention is to pro vide for a process ofstabilizing a crude, saturated cellulose ester by treating it withanhydrous, liquid ammonia at or below its boiling point.

A further object of my invention is to provide for a process ofpurifying and/or stabilizing a crude, saturated cellulose ester bytreating it with anhydrous, liquid ammonia in the presence of anauxiliary agent, said agent being inert to, i. e. incapable ofchemically reacting with, said ammonia.

Other objects of my invention will become apparent to those skilled inthe art from a study of the following specification.

Saturated cellulose esters, i. e., cellulose com-.

pletely esterified with saturated radicals, are conventionally producedby causing alkali metal cellulosates to react with acid halides, such asecetyl chloride, propionyl chloride, etc., or by treating cellulose withorganic acid anhydrides in the presence of acid catalysts. Acidcatalysts commonly used in the esterification of cellulose are forexample, sulphuric acid, nitric acid, hydrochloric acid, thionylchloride, phosphorus pentoxide, phorphorus oxychloride, selenic acid,pyridinium acid sulphate, sulphur dioxide, phosgene, zinc chloride,perchloric acid, sulphoacetic acid, sulphinic acids, halogenated fattyacids, lower molecular fatty acids, halogenated fatty acid anhydrides,naphthalene sulphonic acids, p-toluene sulphochloride, etc. Thisesterification of cellulose may also be carried out in the presence oforganic compounds incapable of dissolving fully esterified cellulose inorder to obtain it in fibrous and/or granular form. Furthermore, thisesterification may be carried out in such a manner that mixed celluloseesters, i. e., esters having at least two different ester groups, areobtained.

However, although these reactions run smoothly in the presence of acidcatalysts, the saturated cellulose esters contain impurities, such aslower substituted esters, side reaction products and catalyst residues,these residues causing discolorill ations of artificial products formedfrom such esters.

Innumerable attempts have been made to stabilize cellulose triacetate insolid form by removing the acidic catalysts contained therein since ithas the valuable property of being more hy-' drophobic that cellulosediacetate. U. S. Patent 1,954,729 to DreyfusLof April 10, 1934,discloses the stabilization of cellulose derivatives by treating themwith an aliphatic alcoholicamineinthepres ence of sodium hypochlorite,etc. U. S. Patent ,091,921 to Malm et al., of November 5, 1935 relatesto a process of stabilizing cellulose triacetate by treating it with apetroleum distillate having a boiling range'of about -200 C. Sindl (videU. S..Patent 2,066,584 of January 5, 1937) stabilizes cellulosetriacetate containing sulphuric acid residues in a swelled state with amixture of a lower fatty acid and a liquid ester of a lower fatty acid.U. S. Patent 2,071,333 to Dreyfus, of February 23, 1 937, removes theacid catalysts by treating crude cellulose triacptate with steam. Alkalifluorides andborates' are used for the same purpose by Ellis et al. asdisclosed in their U. S. Patent 2,072,253 of March 2, 1937. U. S. Patent2,072,260 to Haney, of March 2, 1937, discloses the elimination of acidcatalysts from crude cellulose triacetate by means of water-insolublesalts of basic character. Martin (vide U. S. Patent 2,072,270 of March2, 1937) neutralizes the acid residues with sodium acetate, etc. U. S.Patent 2,095,334 to Jones, of October 12, 1937, relates to a process ofstabilizing cellulose triacetate by passing through it a hot 0.01 to 0.sulphuric acid solution. Malm and Fordyce (vide U. S. Patent 2,095,822of October 12, 1937) remove the acid catalyst of cellulose triacetatewith butyric acid, etc.

Furthermore, I am well aware that cellulose has been rendered morereactive by treating it with liquid'ammonia (vide U. S. Patent 1,173,336to Bronner, of February 29, 1916), and that U. S. Patent 1,966,756taGajewski and 2,012,382 to Fink, disclose the dissolution of fibroin inanhydrous, liquid ammonia. I am also well aware that cellulose diacetatehas been dissolved in liquid, anhydrous ammonia to form solutions fromwhich artificial products may be spun, as set forth for example in U. S.Patent 1,544,809 to Clancy of July 7, 1925, and that nitrogenouscellulose derivatives have been prepared by causing ammonia in anhydrousalcohol to react with cellulose esters having unsaturated radicals inaccordance with a process disclosed in U. S. Patent 2,073,052 toDreyfus, of March 9, 937.

By experimentation, I have unexpectedly found that crude, saturatedcellulose esters can be stabilized by treating them with anhydrous,liquid ammonia. During this treatment the lower substituted celluloseesters are separated from the saturated cellulose esters and the acidcatalysts, contained therein, are removed with the formation ofinoccuous ammonium salts which are either soluble or insoluble inanhydrous, liquid ammonia. Insoluble ammonium salts may be removed fromthe purified esters by washing. Esters formed by chemical interactionbetween acid halides or anhydrides and the acid catalysts are generallyammonolyzed in liquid, anhydrous ammonia. Although I prefer to useanhydrous, liquid ammonia at its boiling point, i. e., at about Y -33C., my process may be carried out at temperatures below 33 C. byevacuating the container in which the crude, saturated cellulose esteris treated with anhydrous, liquid ammonia. In this manner, a completestabilization and purification of a crude, saturated cellulose ester maybe achieved even at a temperature of about --50 C. Furthermore, it isalso within the scope of the present invention to stabilize and purify acrude, saturated cellulose ester by treating it in a closed container atany defined temperature above -33 C. at which it is resistant tochemical attack by anhydrous, liquid ammonia. Each saturated celluloseesterhas such a critical temperature which must be predetermined byexperiment, 4

The stabilization of a crude, saturated cellulose ester, as set forthabove, may also be carried out in the presence of an auxiliary agent ora plurality of auxiliary agents. Auxiliary agents, in accordance with mypresent invention, are such compounds which are miscible with or capableof being dissolved in anhydrous, liquid ammonia without decomposition bychemical reaction, i. e., compounds which are inert to anhydrous, liquidammonia. In addition, these auxiliary agents must be such compounds asare incapable of decomposing the saturated cellulose esters. They may,furthermore, be compounds capable of dissolving incompletely saturatedcellulose esters. These auxiliary agents may be organic or inorganiccompounds, such as benzene, ethers, esters, alcohols, metal nitrates,ammonium salts, metal sulfites, etc. They allow a very prolongedtreatment of saturated cellulose esters at temperatures at we 33 C. withanhydrous, liquid ammonia, and may be added to anhydrous, liquid ammoniato assist in removing incompletely saturated esters contained in crude,saturated esters.

In carrying out my stabilizing, I introduce a crude, saturated celluloseester, either in a dissolved or fibrous form, into a Dewar flask or asimilar container filled with anhydrous, liquid ammonia and let itremain therein until the residual, incompletely saturated esters havebeen disi solved and the acid catalyst neutralized. The

following table depicts the results obtained by varying the duration oftreatment:

About grams of cellulose linters are completely acetylated with 1475 ml.of acetic anhydride in the presence of 40 grams of concentratedsulphuric acid and 2640 ml. of ethyl acetate. The fibrous cellulosetriacetate, after a preliminary wash, contains about 1.78% of sulphuricacid by weight. About 8 grams of this crude triacetate are introducedinto about 300 ml. of anhydrous, liquid ammonia at a temperature ofabout 33 C. for about 4 hours. The fibrous triacetate is separated bydecantation from the Example 11 About 28 grams of propionic acid, 70grams of glacial acetic acid, 150 grams of acetic anhydride (85%), and0.5 gram of sulphuric acid (spec. grav. 1.85) and 50 grams of a purifiedcotton are thoroughly mixed. This mixture is maintained for about 6hours at a temperature of about to 25 C. to form a clear dope. Theproduct is precipitated and washed. It is chloroform-soluble andconsists of fully esterified cellulose acetate propionate containingabout 30% acetyl and 18% propionyl. It contains about 1.2% by weight ofsulphuric acid. About 10 grams of this cellulose acetate propionate areintroduced into about 300 ml. of anhydrous, liquid ammonia for about 5hours. The sulphuric acid content is reduced to 0.013%. The sulphuricacid can be completely removed by prolonged treatment. A suitableauxiliary agent in this treatment is, for example, benzene. Thetemperature at which the stabilization and purification is carried outmay be varied.

Example III About 27.7 grams of sodium stearate are mixed with about10.2 grams of chloracetyl chloride to form an intimate mixture which isheated under reflux at a temperature of about 100 C. for about 6 hours.The mass is filtered while hot with about 200 ml. of ethylene chloride.The filtered ethylene chloride isre-ldded to the mass to which about 0.2cc. of a catalyst, consisting of 1 part by volume of sulphuric acid and3 parts by volume, of phosphoric acid. is added. About 5 grams of acellulose acetate having an acetyl value of about are treated in thismixture for about two days at a temperature of about C. .The clear dopeis diluted with ethylene chloride, filtered and precipitatedin methylalcohol. The

resulting product,\saturated cellulose acetate stearate, dissolves inbenzene and chloroform.

It contains about 2.0% of residual catalyst. After treating thiscellulose acetate stearate for about 20 hours in anhydrous, liquidammonia it is prac tically devoid of acidresidues. for example, may beused as auxiliary. agent.

Although these examples will serve to illustrate my invention, I wish toemphasize that any saturated,celluloseester may be stabilized and/ orpurified in anhydrous liquid ammonia, that the treatment may be carriedout at lower and higher Methyl alcohol} temperatures, that the durationof treatment may be varied within wide limits without decomposing theesters that other auxiliary agents may be in the art, and I desire toinclude'all such modifications and variations coming within the scope ofthe appended claims. In these claims the term crude, saturated celluloseester embraces cellulose esters devoid of free hydroxyl and unsaturatedester groups capable of reacting with anhydrous, liquid ammonia andwhich in addition to acidic residues may also contain other impurities,such as lower substituted cellulose esters, esters formed by chemicalinteraction of acid catalysts and esterifying agents, etc. The termstabilizing embraces the removal of the acidic residues and otherimpurities, such as lower substituted cellulose esters, esters formed bychemical interaction of the acid catalyst and esterifying agents, etc.,from crude, saturated cellulose esters. Furthermore, the term anhydrous,liquid ammonia is intended to comprisethe liquefied gas having theformula NH3 which, how-.

ever, may contain such amounts of water as are unavoidable in theliquefaction when operated on a commercial scale.

I claim:

1. The process of stabilizing a saturated, mixed cellulose ester whichcomprises introducing a saturated mixed cellulose ester into anhydrous,liquid ammonia and subsequently separating said ester from said ammonia,said ester being substantially insoluble in said ammonia.

2. The process of stabilizing a saturated, mixed cellulose ester whichcomprises introducing a saturated mixed cellulose ester into anhydrousliquid ammonia at a temperature of about -33 C. and subsequentlyseparating said ester from said ammonia, said ester being substantiallyinsoluble in said ammonia.

3. The process of stabilizing a saturated, mixed cellulose I ester whichcomprises introducing a saturated mixed cellulose ester into anhydrousliquid ammonia at a temperature below -33 C. and subsequently separatingsaid ester from said ammonia, said ester being substantially insolublein said ammonia.

4. The process of stabilizing a saturated, mixed cellulose ester whichcomprises introducing a saturated mixed cellulose ester into anhydrousliquid ammonia in the presence of an auxiliary agent and subsequentlyseparating said ester from said ammonia, said ester being substantiallyinsoluble in said ammonia.

5. The process of stabilizing a saturated. mixed cellulose ester whichcomprises introducing a saturated, mixed cellulose ester into anhydrousliquid ammonia at a temperature of about -33 C. in the presence of anauxiliary agent and subsequently separating said ester from saidammonia, said ester being substantially insoluble in said ammonia.

6. The process of stabilizing a saturated, mixed cellulose ester whichcomprises introducing a saturated mixed cellulose ester into anhydrousliquid ammonia at a temperature below 33 C. in the presence of anauxiliary agent and subsequently separating said ester from saidammonia, said ester being substantially insoluble in said ammonia.

7. The process of stabilizing a crude, saturated cellulose acetatep-ropion'ate which comprises introducing a solid, saturated celluloseacetate propionate into anhydrous, liquid ammonia and subsequentlyseparating said ammonia from said cellulose acetate propionate.

8. The process of stabilizing av crude, saturated cellulose acetatepropionate which comprises introducing asolid, saturated celluloseacetate propionate into anhydrous, liquid ammonia at a temperature ofabout 33 C. and subsequently separating said ammonia from said celluloseacetate propionate.

9. The process of stabilizing a crude, saturated cellulose acetatepropionate which comprises introducing a solid, saturated celluloseacetate propionate into anhydrous, liquid ammonia at a temperature below-33 C. and subsequently separating said ammonia from said celluloseacetate propionate.

10. A stabilized, saturated, mixed cellulose ester prepared inaccordance with the process set forth in claim 1.

11. A stabilized, saturated, mixed cellulose ester prepared inaccordance with the process set forth in claim 2.

12. A stabilized, saturated, mixed cellulose ester prepared inaccordance with the process set forth in claim 3.

13. A stabilized cellulose acetate propionate prepared in accordancewith the process set forth in claim 1. a

14. A stabilized cellulose acetate propionate prepared in accordancewith the process set forth

